A thermal flow meter that controls the temperature of liquid flowing through a flow passage and measures a flow rate based on a temperature difference between the liquid on an upper stream side of a temperature control portion and the liquid on a downstream side thereof has been heretofore known (e.g., see Japanese Unexamined Patent Application, Publication No. 2006-10322 (hereinafter referred to as “JP 2006-10322”).
JP 2006-10322 discloses a thermal flow meter having a structure in which a glass substrate is provided with a rectangular groove and a flow passage is formed by bonding the glass substrate where the groove is formed to another glass substrate provided with a heating means and a temperature detecting means that are formed on a side of the glass substrate where the groove is formed.